The present invention is an improved method and apparatus to produce a hot fluidizing gas to effect treatment on a material. The method and apparatus are particularly useful for the continuous reaction of hot nitrogen gas for conversion of agglomerates of aluminum oxide and carbon to high purity, ultra-fine aluminum nitride powder.
A method presently known to react a gas with a particulate solid is a fluid bed reactor. In that reactor, a gas is introduced at the bottom of a reaction vessel and travels upward to fluidize particulate material or agglomerates that are introduced from the top of the reaction vessel. Prior fluid bed reactors and methods have several disadvantages when a hot fluidizing gas is required such as when reacting aluminum oxide and carbon with nitrogen to form aluminum nitride. In order to have a heated fluidizing gas to effect treatment, the gas must be at the proper temperature when in the reaction chamber. There are two methods to achieve proper gas temperature in the reaction chamber. One method is to heat the gas externally with no heating occuring in the reactor. The second method is to heat the gas internally. Either method has some disadvantages.
Preheating a gas to high temperature (over 1000.degree. C.) before it enters the fluid bed reactor is very difficult because of the problems of transporting a gas this hot. Indeed, preheating a fluidizing gas to a temperature of 1500.degree. C. or more has not been commercially practical. On the other hand, if the gas is not preheated, but is instead heated within the reactor, an insufficiently heated gas can quench the reaction, an acute problem when the process involves an endothermic reaction. Heating the gas within the reaction chamber has not been entirely satisfactory, mainly because of the difficulty of maintaining a high constant temperature in a continuous reaction.